Recently, various low power wireless devices using an industrial, scientific and medical (ISM) band and an unlicensed national information infrastructure (UNII) band that are useful without a license have been researched and developed. Specifically, an audio wireless transmitting device such as a wireless microphone, a wireless headphone and a wireless speaker uses the ISM band or the UNII band. In addition, a digital video wireless transmitting device such as a wireless internet broadcasting and a wireless surveillance camera uses a wireless technology such as a wireless local area network (LAN), a Bluetooth and a frequency shift keying (FSK) transceiver. Moreover, a standard IEEE 802.11n that expands a distance of a wireless LAN using a multiple-in multiple-out (MIMO) antenna has been suggested and an access point (AP) device using the MIMO technology has been come out.
However, since the ISM band or the UNII band is utilized without any limitation in usages and authorities, a transmission quality may be severely deteriorated due to interference when various application devices are simultaneously used in a given area. Further, even when a single application device is used in a given area, a fading phenomenon due to a multi-path signal reflecting on adjacent surroundings occurs because of a transmission method using a low power and a high frequency. As a result, the transmission quality is deteriorated and the transmission range is restricted. In addition, since the sensitivity varies according to direction, various digital wireless devices have not been suggested and released sufficiently in an application device field requiring a realtime transmission of high quality. For example, a wireless microphone for a karaoke, a broadcasting, a stage or a conference may have an infrared type or an analog type. The analog wireless microphone has disadvantages such as a poor sound quality, a limitation of simultaneous users due to insufficient channels and a low value added functions of various requirements, e.g., an additional information exchange. However, since the problems of the digital wireless microphone such as a limitation in transmission range and an error due to a fading phenomenon by a multi-path are not solved, the analog wireless microphone is still widely used.
To solve the above problems, a transmission method using a MIMO antenna and a diversity method of frequency, time or antenna where a transmission speed is improved and audio/video of non-compressed high quality are transmitted have been suggested. As a result, transmission range is improved as compared with a wireless LAN according to the related art. However, the device transmitting a high frequency signal in the ISM band or UNII band with a relatively low power has substantial limits in a transmission range, and the errors due to the fading phenomenon are not improved. In addition, an ultra wide band (UWB) technology that is recently commercialized in an audio field has a disadvantage such that the transmission range is relatively short as compared with a wireless LAN.